Climate models project a striking reversal in the Pacific Ocean's oxygen distribution, according to a modeling study published in AGU Advances. In the subtropical North Pacific, where oxygen is currently abundant, warming and stratification compress the gyre and reduce ventilation, causing dissolved oxygen to decline and making the water mass appear older. Meanwhile, in the tropical Pacific, reduced upwelling of old, low-oxygen water means the water becomes younger and gains oxygen.
The mechanism traces to a slowdown of vertical velocities driven by heat forcing from both the Pacific basin and the remote Southern Ocean. The authors, led by Taylor et al., find that mid-latitude Southern Ocean warming weakens the upwelling that carries old, oxygen-poor water into the tropics and North Pacific. This combined forcing sets up the paper's counterintuitive conclusion: "young gets older, but old gets younger."
The study relies on model projections rather than observations, so the exact magnitudes remain uncertain. But the results highlight how warming can reshape ocean circulation and biogeochemistry in opposing ways across different regions of the same basin.